This invention relates to a process for treating a radioactive waste, and more particularly to a process for treating a radioactive liquid waste, suitable for shaping pellets having a low hygroscopicity.
Heretofore, radioactive liquid wastes produced in radioactive material handling facilities of nuclear power plants, etc. have been classified according to their characteristics, and treated or stored. For example, a large amount of radioactive liquid wastes in a solution state produced in boiling water-type nuclear power plants, such as a liquid waste resulting from regeneration of ion exchange resin, which contains sodium sulfate (Na.sub.2 SO.sub.4) as a main component, etc. is solidified by cement or asphalt in drums. Used ion exchange resin, filter aid, etc. are stored in tanks in a slurry state. Thus, in order to reduce storage space, attempts have so far been made to dry the radioactive liquid waste in the slurry state into powder by a drier such as a thin film drier, etc., then pelletize the powder into pellets by a pelletizer such as a briquetting machine, etc., and storing the pellets, thereby reducing a considerable volume of the radioactive wastes coming from the nuclear power plants as the effluent. In that case, it is necessary to prevent the pellets from breakage or scattering as powder, etc. at the transportation or handling such as the filling into drums, etc.
Japanese Laid-open Patent Application Specification No. 93865/75 (laid open on July 26, 1975) discloses a process for treating a radioactive liquid waste by means of a binder so as to increase the strength of the pellets, where a radioactive liquid waste containing the binder is dried into powder by a spray drier, the powder is shaped into pellets, and the pellets are stored in storage tanks.
A process for treating a radioactive liquid waste to reduce the number of drums containing pellets solidified by asphalt is proposed in Japanese Laid-open Patent Application Specification No. 34200/77 (laid open on Mar. 15, 1977), where a radioactive liquid waste is made into powder, the powder is shaped into pellets, the pellets are stored for a specific period, and the pellets whose radioactivity is reduced by the storage are filled into drums, and solidified by asphalt. According to said process, number of pellets to be filled in a drum can be increased, and thus the number of the required drums can be reduced, as compared with the case of filling the pellets into drums immediately after the shaping. However, the stability of pellets must be maintained during the storage, and it is necessary to prevent the pellets from deliquescence, moisture absorption, etc. However, the pellets prepared according to the conventional processes are very unsatisfactory in meeting said requirements.
To overcome these disadvantages, a process of impregnating pellets with a liquid plastic monomer such as styrene monomer, adding a polymerization initiator such as benzoyl peroxide thereto, and polymerizing the monomer is proposed in Japanese Patent Publication No. 8880/78 (published on Apr. 1, 1978), where an apparatus for impregnating the pellets with the liquid plastic monomer and the polymerization initiator is required, which complicates the system, and furthermore it is difficult to impregnate the individual pellets with the liquid plastic monomer and the polymerization initiator continuously and rapidly. For example, the impregnation will be quite inefficient when carried out one by one, and the number of the pellets waiting for the impregnation is increased. Furthermore, when the polymerization is carried out while placing the pellets, for example, on a plate, the pellets themselves will adhere to the plate, and when a plurality of the pellets are in contact with one another, the plurality of the pellets will adhere to one another. Thus, the handling must be inevitably made with much care.